ESA astronaut Thomas Pesquet during International Space Station spacewalk maintenance 2 training at the Neutral Buoyancy Laboratory.
Thomas exchanged some of the Space Station heat exchangers that interface the internal cooling loops collecting heat loads, and external ammonia cooling loops that reject heatt via the radiators.
The exchangers are underneath the micro meteorite shields so hard to get to.
Another task involved exchanging ammonia tanks. These tasks are part of 12 major failures that would force an astronaut to go out the door in a short amount of time to repair, and need to be rehears in the NBL pool before flight.